1. Field of the Invention
This invention relates to a thermochromic material and a heat sensitive recording material based on the thermochromic material.
2. Description of the Prior Art
Various thermochromic compounds which change in color due to change in temperature are known. Examples of known thermochromic compounds include inorganic compounds such as CoCl.sub.2, 2(CH.sub.2).sub.6 N.sub.4.10H.sub.2 O, PbCrO.sub.4, etc., and organic compounds such as the spiropyrans, bianthrone, dixanthylene, chloresteric liquid crystals, etc. Such compounds are used as temperature indicating paints, etc.
Except for a few examples, these compounds cannot meet the practical requirement of the ability to visually indicate temperature differences since they have various drawbacks, including a rather rapid deterioration during repeated temperature cycling, insufficient color change, a poor fastness to ultraviolet light, a relatively high cost, etc.